The study was carried out in seven white cats exhibiting a unilateral hereditary deafness. Transneuronal degeneration in the primary cochlear nuclei was investigated by measuring the areas of various types of cells in the side corresponding to both the deaf and the normal ear. Four types of cells were selected, namely: pyramidal cells in the dorsal cochlear nucleus, octopus cells in the posteroventral cochlear nucleus, large spherical cells in the anteroventral cochlear nucleus, and globular cells in the interstitial nucleus. The sample consisting of at least 100 cells of each type, on each primary cochlear nuclei of each animal was completely randomized. The cell was amplified and drawn 800x and the area of both cell body and nucleus measured with a planimeter. The area of the nucleolus was calculated after measuring its diameter. The neurons corresponding to the deaf ear showed a reduction in area of about 33 percent relative to the area of controls. The evidence indicates that transneuronal degeneration of the second order auditory neurons may be related to a retardation in growth rather than atrophy following sensory deprivation.